> Modern sheep grow their wool continuously, but that took a while to breed in.

No they don't.

In the summer their wool starts to grow out much thinner, like maybe a quarter as thick - it's really noticeable. This gives what's called a "rise", a gap between the sheep's skin and the thicker coarser wool. Once that's high enough to get shears (or these days, machine clippers which are like a big beard trimmer) into you can shear the fleece off.

If there's no rise you haven't a hope in hell of cutting it.

If there's a good rise it practically falls off.

If you leave them long enough or if the rise starts growing in too soon, they'll start "casting" where their wool just falls off in big chunks. This is actually quite dangerous for them because it's itchy and they roll on their backs to scratch, and get stuck upside down with their legs in the air and suffocate.

And you thought sheep farming was easy and fun ;-)